Carburetor



Dec. 18, 1934. A. M. PREN'rlss 1,984,382

CARBURETOR Filed Jan. 25, 1932 2 Sheets-Sheet l I N V EN TOR. Qua/s 77/V MPEE/VT/SS A TTORNEY Dec. 18, 1934. A. M. PRENTISS GARBURE'IOR Filed Jan. 25, 1932 2 Sheets-Sheet 2 I IN VEN TOR. 670605 77/v M. PEEA/WSS BY 4 $212 A TTORNEY Patented Dec. 18, 1934 UNITED STATES PATENT OFFICE cmunn'ron Augustin M. Prentiss, San Antonio, Tex. Application January 25, 1932, Serial No. 588,758

15 Claims. .(Cl. 201-72) This invention pertains to carburetors and more particularly has reference to pressure feed carburetors of the compensating type;

This invention is an improvement upon the inventions disclosed in my United States Patent 1,329,309, issued January 27, 1920, and in my copending application Serial No. 590,292, filed February 1, 1932.

In the patent referred to I pointed out the advantages that resulted from the use of atomizing nozzles for feeding the liquid fuel into the mixing chamber of the carburetor, whereby the liquid fuel was fed under a superatrnospheric pressure, and compressed air was used to break up the liquid fuel within the nozzle so that it issued in the form of a fine spray or fog. I also discussed the difficulties of securing uniformity in the fuel-air mixture due to the differences in the laws of liquid and gas flow and pointed out various corrective methods used in the prior art without success. I then indicated one solution of the problemlwhich proved satisfactory.

In the copending application referred to, I disclosed another solution of the problem of securing compensation of the fuel-air mixture when the fuel and part of the air component were fed into the mixing chamber under superatmospheric pressure.

I have since found that certain additional ad vantages accrue if all of the air component is fed into the mixing chamber under a superatmospheric pressure and in this application I disclose a novel means of effecting this result and at the same time securing compensation of the fuel-air mixture so that its composition can be controlled under all operating conditions.

An object of this invention is to devise a carburetor wherein all the air component is fed into the mixing chamber under such a variable, controlled, superatmospheric pressure that the ratio of the liquid fuel to air may be controlled under all operating conditions.

Another object of this invention is to devise a carburetor wherein both the liquid fuel and air components are fed into the mixing chamber under variable controlled superatmospheric pressures whereby the ratio of liquid fuel to air may be maintained at any desired value under all op- 5n crating conditions.

Still another object of this invention is to provide an improved device having means for supplying air under a superatmospheric pressure to the liquid fuel within the fuel nozzle to break up the liquid fuel column before it issues from the of the liquid fuel.

With these and other'obiects in view which may be incident to my improvements, my invention consists in the combination and arrangement of elements hereinafter described and illustrated in the accompanying drawings in which:

Figure 1 shows in central longitudinal section a carburetor embodying my improvements, and

Figure 2 shows in side elevation my improved carburetor in operative connection to the main fuel supply tank and compressed air pump.

Figs. 3 and 4 are fragmentary views of certain pressure control valves in applicants device.

Unless specially controlled and regulated to the contrary, the flow of liquid fuel through a carburetor follows the general law of liquid flow and the how of air follows the law of adiabatic gas flow. As to the air flow, it is logical to assume that the expansion of a gas approaching an orifice; being rapid, is adiabatic, and the authorities generally agree that the flow of air through a carburetor is, for all practical purposes, sensibly adiabatic. support this view.

The observed data The general formula for liquid flow and adiabatic gas flow, as applied to a carburetor, may

be expressed as follows G1 is the rate of liquid flow in pounds per second.

G2 is the rate of air flow in pounds per second. ,ui is the coefficient of eillux for liquid flow. a: is the coefficient of eiilux for adiabatic gas flow.

F1 is the cross-sectional area of the liquid fuel passageway of the carburetorgenerally the sageway.

F2 is the cross-sectional area oi the main air area of the metering restriction in the fuel paspassageway of the carburetor in the zone of the fueljet orifice-generally the area of the smallest section of the Venturi throat.

' 1 is the unit weight of the liquid fuel, in

a is the acceleration of gravity.

Po is the superior pressure causing the fluid flow, which, in suction-operated carburetors, is the atmospheric pressure outside the carburetor.

Pm is the absolute pressure in the mixing chamber of the carburetor in the zone of the fuel jet orifice.

The foregoing nomenclature and formulas are in accordance with Church's Mechanics of Engineering; Part IV, Chapter VIII on Kinetics of gaseous fluids.

For convenience of reference in this speciflcation, I shall follow Churchs terminology and refer to the formula for liquid flow (Formula (1) above), as the water formula and the formula for air flow, (Formula (2) above), as the "adiabatic formula. It will also be understood that where I refer, in this specification, to the air supply to the mixing chamber of the carburetor as being fed into said chamber in accordance with the law of liquid flow", I mean in accordance with thewater formula (Formula 1) above). That is to say, the total weight of air passing into the mixing chamber, per unit of time, for any given pressure (vacuum) in said chamber, is that found from the water formula" 1) above) for Pm equal to the pressure (vacuum) in said chamber, and not from the adiabatic formula ((2) above) which normally governs the flow of air through a carburetor.

It will be further understood that where I refer, in this specification, to the air supply to the mixing chamber being fed into the mixing chamber in accordance with the normal law of air or gas flow, I mean in accordance with the "adiabatic gas formula" (Formula (2) above) and where I use the term normal operating conditions I mean conditions of steady flow through the carburetor which excludes momentary fluctuatlons due to sudden changes in throttle opening.

This invention broadly comprehends a carburetor having the general features and operating principles disclosed in my patent and copending application referred to and, in addition thereto, means for feeding the whole of the air component into the mixing chamber under such a variable, controlled, superatmospheric pressure as will result in perfect compensation of the fuelair mixture, so that its composition may be regulated and maintained at any desired quality under all operating conditions. By introducing the whole air component under a superatmospheric pressure I not only secure a corresponding supercharging effect but also an improved engine performance at slow speeds and quick acc'eleration.

Referring to Figure 1 of the drawings, the reference numeral 1 denotes the body of a carburetor having a main air inlet 2, Venturi throat 3. mixing chamber 4 and mixture outlet 5 controlled by a butterfly throttle valve 6 in the usual manner. Integral with the bottom wall of the body 1 and extending to a point just above the center of the Venturi throat 3. is an atomizing nozzle 7, consisting of an outer liquid fuel tube 8, and an inner air tube 9. Surmounting tube 8 and adjustably attached thereto by screw threads is a cap 10 having a central aperture 11 through which liquid fuel and air from tubes 8 and 9' are discharged into the mixing chamber.

Tube 8 communicates through a passageway 12 with liquid fuel reservoir 13 which is supplied with liquid fuel under superatmospheric pressure from a pipe 14 through an inlet 15 controlled by a valve 16 which is actuated by a float 17 in the usual manner so as to maintain the liquid fuel in reservoir 13 at a constant level XX. Float 17 has sufficient buoyancy to always close valve 16 against the pressure of the liquid fuel in pipe 14 whenever the liquid level in reservoir 13 rises above the line X-X. Passage 12 is controlled by a. manually adjustable needle valve 18 which is threaded through the wall of reservoir 13 and held in adjusted position by a lock nut 19 which also acts as a gland nut to compress packing 20 and prevent the leakage of liquid fuel around the threads on valve 18. Valve 18 regulates the flow of liquid fuel from reservoir 13 to nozzle 7 and thus determines the quality of the fuel-air mixture.

Reservoir 13 is closed at the top by a cover 21 which seats on a gasket 22 and is held in place by a series of screws 23. Extending downwardly from the under side of cover 21 is a screw threaded boss 24 to which is attached a short cylindrical sleeve 25 which acts as a cylinder for a piston 26. Screw-threaded to piston 26 is a tapered valve stem 27 which passes through a correspondingly tapered valve seat 28 in the cover 21 and is adapted to regulate the escape of air from reservoir 13 by varying the size of vent 28 as it is moved up and down by piston 26. Interposed between piston 26 and a partition 29 in cylinder 25 is a helical spring 30 which tends to move piston 26 downwardly against the pressure of the air in reservoir 13. At the top of sleeve 25 is a plurality of ports 31 which establish communication between cylinder 25' above partition 29 and reservoir 13 and whose total area exceeds the maximum area of vent 28. That part of valve stem 2'? which reciprocates through partition 29 is cylindrical and fits partition 29 with an air-tight fit. The purpose and function of valve 27 will be hereinafter more fully explained.

Air tube 9 communicates through a passageway 32 with an auxiliary air chamber 33 which is supplied with compressed air through a pipe 34 by a constant-pressure rotary pump 35 which is geared by a worm drive 36 to the engine (not shown). See Figure 2. Chamber 33 also communicates through an opening 37 in a partition wall 38 with a cylindrical chamber 39 in which reciprocates a piston 40 having attached a sleeve valve 41 which serves to regulate the communication between chamber 33 and cylinder 39, as clearly shown in Figure 1. Sleeve valve 41 is closed at its lower end and has in its side wall a triangular-shaped port 42 whose side edges are curved so that as piston 40 moves valve 41 down into chamber 33 a progressively increasing area is exposed to chamber 33 below partition 38 for a purpose to appear hereinafter.

Interposed between piston 40 and the top of cylinder 39 is a helical spring 44 which tends to push piston 40 downwardly in opposition to the vacuum in the top of cylinder 39 which is transmitted from mixing chamber 4 by a passageway 45. A lug 46 on the upper edge of piston 40 limits its upward travel and prevents its cutting off passageway 45.

Compressed air escaping from chamber 33 through valve 41 into cylinder 39 is returned through'a pipe 47 to inlet pipe 48 of pump 35. A flap valve 49 alternately opens and closes pipes 47 and 48 depending upon the relative air pressures in each, as shown in Figure 2.

A pipe 50 leads from pipe 34 to a main liquid fuel supply tank 51 through a'check valve 52 and maintains a superatmospheric pressure in tank 51 equal to that in pipe 34. This pressure lifts the liquid fuel from tank 51 to the reservoir 13 of the carburetor and thus makes unnecessary any pump or special fuel lifting device.

Chamber 33 communicates with reservoir 13 through a passageway 53 which serves to transmit the air pressure in chamber 33 to reservoir 18.

A section 54 of the outer wall of cylinder 39 is removable to provide access to the interior of cylinder 39 so that piston 40 and valve 41 can be assembled therein and removed therefrom. Panel 54 is held in air tight fit in cylinder 39 by any suitable means such as straps, screws, etc. (not shown). Instead of transmitting the variable air pressure of chamber 33 to reservoir 13,1 may, as an alternative mode of operation subject the liquid fuel therein to a constant superatmospherio pressure taken from air pipe 50 (Figure 2) and transmitted to said reservoir through a pipe 55,.

reducing valve 56, pipe 57 and passageway 58. As this pressuFe need only be very low (say two or three pounds, gauge) a reducing valve (as 56) must be usedto reduce the pressure from that in pipe 50 to the lower pressure required, whenever the pressure in pipe 50 exceeds the pressure desired in reservoir 13. Some reduction in pressure is always necessary in order that the fuel in tank 51 may be lifted to reservoir 13 and fed thereinto against the air pressure therein.

The operation of my device is asfollows: with the engine at rest the liquid level in the reservoir 13 is at X-X and flap valve 49 is in horizontal position by gravity; alsoif supply tank 51 has not been refllled'with liquid fuel since the previous operation of the engine, check valve 52 will retain therein the air pressure previously supplied by pump 35. If tank 51 has been refilled and the air pressure therein released, there is suillcient fuel in reservoir 13 to run the engine long enough for pump 35 to reestablish operating air pressure in tank 51.

When the engine is started, the first few revolutions either by the starter, or the engine under its own power, is sufllcient to enable pump 35 to supply an adequate stream of compressed air to nozzle 7 to, atomize the liquid fuel issuing therefrom. Pump 35 is of sumcient capacity to supply the maximum volume of air required by the engine at all speeds and under all operating conditions, and, being geared to the engine, its rate of air supply automatically keeps pace with the demands of the engine. Pump 35 is also of the self-regulating constant-pressure type so that as soon as the engine has gained a certain predetermined speed (preferably just above idling) pump 35 maintains a constant pressure on the air line 34. w

Air under constant pressure which may be regulated by suitable adjustment on pump 35 is thus supplied to chamber 33 at all times while the carburetor is in operation. The amount of pressure on the air supply is a matter of choice. Only a very nominal pressure (say two or three pounds per square inch) is required to atomize the liquid fuel issuing from nozzle 7, but there are some advantages in further increasing this pressure, viz. smaller air pipes (34 and 37) and even a smaller size of Venturi throat 3 is required as the pressure is increased, also there are corresponding supercharging efl'ects with increased pressure. For the purpose of illustration, it will be assumed that pump 35 is set to maintain a gauge pressure of one atmosphere (say 15 pounds per square inch) in line 34.

When the engine first startsup, the throttle 6 is slightly opened and the engine turned over by the starter. Under these conditions the vacuum in mixing chamber 4 is small and hence valve 41 is held by spring 44 in its lowermost position with port 42 fully exposed to chamber 33. Since the areaof port 42 is equal to, or may even exceed, the area of pipe 34 and also the area of port 2 is equal to, or may exceed, the area of pipe 34. it follows that the compressed air in chamber 33 may escape at a faster rate than it can be supplied by pipe 34 and hence there will'be a large drop in pressure in chamber 33, so that the pressure therein is only slightly above atmospheric. At the same time, this pressure, regardless of its actual value, is transmitted to reservoir 13 through passageway 53, and acts upon the liquid fuel in said reservoir forcing it to feed from tube 8 and nozzle 7 into the mixing chamber 4.

As the throttle is opened and the speed of the engine increases the vacuum in the mixing chamber correspondingly increases and valve 41 is progressively raised by the increased vacuum in cylinder 39. As valve 41 rises it cuts ofl from chamber 33 a progressively increasing area of the port 42 since the sides 43 of this port are curved, and this in turn causes a corresponding rise in the pressure of the air in chamber 33, as the ratio of exit ortage to inlet portage is decreased. Since passageway 45 joins mixing chamber 4 at the most constricted zone of Venmaximum which approaches the pressure in line 34 as a limit. Thus the air supply is maintained under a superatmospheric pressure which varies from just above atmospheric pressure to the full pressure exerted by the air pump (here assumed to be 15 pounds per square inch). Under this pressure, approximately twice the flow of air would occur through the carburetor as would occur if the air were drawn in at atmospheric pressure. For this reason the Venturi throat 3. mixing chamber 4 and mixture outlet 5 need be made only about half the size of those required for a suction operated carburetor. This greatly improves operation at low speeds, since the smaller size of Venturi maintains a better suction on the liquid fuel jet issuing from nozzle Since the ratio of the pressure in chamber 33 to the vacuum in the mixing chamber is dependent upon the configuration of port 42 in valve 41, and the sum of this pressure and vacuum control the flow of air through the carburetor, it follows that the rate of this air flow can be made to vary as desired by varying the configuration of port 42.

As the pressure in chamber 33 is transmitted to reservoir 13 through passage 53, the variations in pressure in chamber 33 would be effective upon the liquid fuel in reservoir 13 if not modified by valve 27. But, since I have shown reservoir 13 will not increase at the same rate, or as fast a rate, as the pressure in chamber 33. This is the function of valve 2'7. As the pressure in reservoir 13 rises, piston 26 is pushed up raising valve 2'? and permitting a portion of the air in reservoir 13 to escape into the outside atmosphere. This correspondingly relieves the air pressure in reservoir 13 and the ratio of the air pressure in reservoir 13 to that in chamber 33 can be made to vary as desired by a propercurving of the valve stem 27 which controls the outlet 28. In this way the pressure on the liquid fuel in reservoir 13 can be made to vary as required in order to compensate for the inherent difference between the law of liquid flow and gas flow, so that the quality of the fuel-air mixture may be controlled as desired under all operating conditions. 1

Since only a slight amount of air need be discharged through port 28 in order to regulate the pressure in reservoir 13, its effect upon the pressure in chamber 33 is negligible.

Since the air escaping from chamber 33 into cylinder 39 is returned to pump through pipe 47 under a slight superatmospheric pressure, as long as any such air is returning through pipe 47, it will force valve 49 to its horizontal position and cut off the air supply from the outside atmosphere through pipe 48. In this way, the pressure of air in pipe 47 is not lost and helps to reduce the load on the pump 35.

When the throttle 6 is suddenly kicked open for a quick acceleration, the sudden increase in vacuum in mixing chamber 4 immediately closes valve 41 and this in turn immediately increases the pressure in chamber 33 and reservoir 13 with a corresponding increase in air and liquid fuel supplied to the mixing chamber. Since the valve 2'7 has some inertia it does not instantly relievethe sudden increase in pressure in reservoir 13 and hence there results a momentary superfective in securing rapid acceleration. For this reason no special acceleration device is necessary.

The pressure in chamber 33 may be so varied, as explained above, that the air supply to mixing chamber 4 will be fed thereinto in accordance with the law of liquid fiow. In such a case. communication between chamber 33 and reservoir 13 is cut off by a valve at 59 shown in Figure 3, and the liquid fuel in said reservoir is subjected to a constant superatmospheric pressure through pipes 55 and 57 and reducing valve 56. In this case, valve 27 is unnecessary and may be rendered inactive by forcing it down into vent 28 so that it .will be held fast by any suitable means. Compensation of the fuel-air mixture is now secured by causing the air supply to flow in accordance with the same law' of flow as the liquid fuel, the pressure on the air supply being suitably varied for this purpose.

While I have shown and described the preferred form of my invention,'I desire it to be understood that I do not limit myself to the precise details of construction disclosed, as these may be readily changed and modified by those skilled in the art without departing from the spirit of my invention or exceeding the scope of the appended claims.

I claim:.

1. In a carburetor, a mixing chamber, a liquid fuel supply thereto under a constant superatmospheric pressure, and means for supplying ,air thereto under such a variable superatmospheric pressure that the two supplies always hear a desired predetermined ratio to each other under all operating conditions.

2. In a carburetor, a mixing chamber, a liquid fuel supply thereto under a superatmospheric pressure, an air supply thereto under a superatmospheric pressure and means for maintaining such a difference between the pressures on these supplies as to make said supplies always bear a desired predetermined ratio to each other, under all operating conditions.

3. In a carburetor, a mixing chamber, a liquid fuel and an air supply thereto, both under a common superatmospheric pressure and means to modify this pressure on the liquid fuel supply so that said fuel supply will always bear a desired predetermined ratio to said air supply under all operating conditions.

4. In a carburetor, an atomizing nozzle, an air supplythereto, and means for subjecting said air supply to such a variable superatmospheric pressure that said supply will be fed into said nozzle at a rate which varies in accordance with the law of liquid flow.

5. In a carburetor, an atomizing nozzle, 9. liquid fuel and an air supply thereto, both under a common variable superatmospheric pressure, and means to modify this pressure on the liquid fuel supply so that said fuel supply will always flow through said nozzle in a desired predetermined ratio to said air supply under all operating conditions.

.6. In a carburetor, a mixing chamber, a liquid fuel supply thereto, and means for supplying compressed air thereto under such a variable pressure as will always maintain a predetermined ratio between the rates of fiow of said liquid fuel and air supplies.

'7. In a carburetor, a mixing chamber, an atomizing nozzle associated with the mixing chamber, means for supplying liquid fuel under superatmospheric pressure to said nozzle, means for supplying air under superatmospheric pressure to said nozzle, and an automatic meansfor regulating the pressure on the air supply to said nozzle.

8. In a carburetor, a mixing chamber, means for supplying thereto air under a superatmospheric pressure, and means for so controlling said pressure that said air supply will be fed into said chamber at a rate which varies in accordance with the law of liquid flow.

9. In a carburetor, a mixing chamber, means for supplying thereto air under a superatmospheric pressure, and means responsive to the pressure in said chamber for so controlling said superatmospheric pressure that said air supply will be fed into said chamber at a rate which varies in accordance with the law of liquid flow.

10. In a carburetor, a mixing chamber, a compressed air supply thereto, a liquid fuel supply thereto under pressure from said compressed air and means for maintaining such a difference between the pressures on these supplies as to make said supplies always bear such ratios to each other as to form a mixture of desired predetermined composition under all operating conditions.

11. In a carburetor for internal combustion engines, a mixing chamber, a compressed air supply thereto, a liquid fuel supply thereto under pressure from said compressed air and means for maintaining such a difference between the pressures on these supplies as to make said supplies form a mixture of constant composition under all operating conditions except at lowest and highest speeds of the engine.

12. In a carburetor, a mixing chamber, means for supplying thereto liquid fuel and air under superatmospheric pressures, and means for varying said pressures, relative to each other, so that said liquid fuel supply bears a predetermined ratio to said air supply under all operating conditions.

13. In a carburetor. a mixing chamber having an atomizing nozzle therein, a liquid fuel supply to said chamber under a constant superatmospheric pressure, and an air supply to said chamber under such a variable superatmospheric pressure that the two supplies always hear a desired predetermined ratio to each other under all operating conditions, all of said liquid fuel supply and part of said air supply being fed into said chamber through said nozzle.

14. In a carburetor, a mixing chamber having an atomizing nozzle therein, a liquid fuel supply to said chamber under a constant super atmospheric pressure, an air supply to said chamber under a superatmospheric pressure, all of said liquid fuel supply and part of said air supply being fed into said chamber through said nozzle, and means for maintaining such a difference between the pressures on these supplies as to make them always bear a predetermined ratio to each other under all operating conditions.

15. In a carburetor, a mixing chamber having an atomizlng nozzle therein, a liquid fuel and an air supply to said chamber, both under a common, variable, superatmospheric pressure, all of said liquid fuel supply and part of said air supply being fed into said chamber through said nozzle, and means to modify the pressure on the liquid fuel supply so that said fuel supply will always bear a definite predetermined ratio to said air supply under all operating conditions.

AUGUSTIN PRENTISS, 

